1. Field of the Invention
The present invention relates to a method and apparatus for changing the line in a printer, in particular in a serial printer.
The present invention can be applied to the printing of both cut sheets and continuous sheets with perforations on each side of the sheet. These continuous sheets will be referred to hereinafter as fanfold paper.
In a serial printer which prints, for example, a cut sheet, after the cut sheet is loaded on a rear cover of the printer, the sheet is fed forward in accordance with a command to start printing from a line change drive control unit, so that a platen rotates to move the sheet with the help of pinch rollers. During the movement of the sheet, the sheet is sensed by a sensor, which is located on the passageway of the sheet to detect passing of the front end of the sheet.
A further movement of the sheet is carried out through a predetermined displacement from the point of the detection to bring the sheet to a print starting position, at which the printing is commenced. The sheet set at the print starting position is printed by a printing head carried on a carriage which moves along the platen. The sheet is fed forward line by line by the rotation of the platen.
2. Description of the Related Art
Generally, when the sheet is located in the print starting position, the front end of the sheet is held between the platen and bail rollers which, together with the rotating platen, feed the sheet forward.
Namely, there is a vacant space at the front end (leading end) of the sheet, corresponding to a distance L between the front edge of the sheet and the portion of the sheet that is located in front of the printing head. That is, when the sheet is located at the print starting position, the front edge of the sheet passes the printing head by the distance L. Therefore, when the printing is completed for one sheet, there is always a vacant space (non-printed area) corresponding to the distance L at the front end of the sheet.
On the contrary, if the printing is commenced immediately the front edge of the sheet reaches the printing head, often the front end of the sheet is not held between the bail rollers and the platen when the front end of the sheet reaches the bail rollers during the forward movement of the sheet. This results in a paper jam.